This invention relates to a recording medium driving device for rotationally driving a disc-shaped recording medium and thus recording and/or reproducing digital data to and/or from the disc-shaped recording medium, and a tilt detection method for detecting the tilt quantity generated in rotationally driving the disc-shaped recording medium.
As recording media on which digital data is optically recorded, optical discs such as so-called CDs (compact discs) and DVDs (digital versatile discs or digital video discs) are broadly known.
In an optical disc drive device for recording and/or reproducing digital data to and/or from such optical discs, an optical disc that is rotationally driven is irradiated at a desired position with a minute spot of a condensed laser beam by an optical pickup, thus recording and/or reproducing digital data. In this case, the optical pickup operates with the laser beam tracing a track provided on the optical disc so as to stably record digital data onto the optical disc or reproduce digital data recorded on the optical disc with high fidelity.
Meanwhile, a radial tilt might be generated in the above-described optical disc because of the warp of the optical disc or the inclination of the optical pickup in the optical disc drive device due to the environmental influence such as the temperature and humidity at the time of use and/or storage and the handling state. It is known that such a tilt causes aberration of the regenerative optical spot and therefore brings about distortion of reproduced signals, lowering of the MTF (modulation transfer function), and lowering of the recording power efficiency.
Recently, in optical disc drive devices, the numerical aperture (NA) of the objective lens of the optical pickup tends to be increased for higher density of the optical disc. For example, an objective lens with an NA value of 0.45 is used for CDs and an objective lens with an NA value of 0.60 is used for DVDs. Accordingly, the thickness of the optical disc has been reduced. Thus, the optical disc is likely to warp and has a large NA value, and therefore has increasingly large angular dependency of aberration.
On the other hand, an optical disc drive device which has a dedicated sensor to detect the tilt quantity and incline the objective lens or actuator in its optical pickup on the basis of the detection signal for compensating a tilt has been provided for practical use.
However, if an optical disc of a small diameter is used, the conventional optical disc drive device cannot sufficiently secure the place for installing the sensor for detecting tilt quantity and it is therefore difficult to detect the tilt quantity.
In view of the foregoing status of the art, it is an object of the present invention to provide a recording medium driving device and a tilt detection method which can solve the problem of the tilt detection system of the conventional optical disc drive device and detect the tilt quantity from a signal obtained from the optical pickup quickly and with high accuracy.
A recording medium driving device according to the present invention is adapted for rotationally driving a disc-shaped recording medium in which signal information that can be discriminated from recording data is recorded on one of both sidewalls of a recording area having the recording data recorded thereon, and recording and/or reproducing digital data to and/or from the disc-shaped recording medium. The device comprises: optical pickup means for casting a laser beam onto the disc-shaped recording medium and receiving a return light reflected and diffracted on the surface of the disc-shaped recording medium; amplitude detection means for detecting the amplitude of a signal based on a return light from the signal information recording sidewall, which is the sidewall having the signal information recorded thereon; and tilt detection means for detecting the tilt quantity on the basis of the amplitude of the signal detected by the amplitude detection means.
In the recording medium driving device according to the present invention, the tilt quantity is detected on the basis of the return light from the signal information recording sidewall of the disc-shaped recording medium.
A tilt detection method according to the present invention comprises the steps of: casting a laser beam onto a disc-shaped recording medium in which signal information that can be discriminated from recording data is recorded on one of both sidewalls of a recording area having the recording data recorded thereon, and receiving a return light reflected and diffracted on the surface of the disc-shaped recording medium; detecting the amplitude of a signal based on a return light from the signal information recording sidewall, which is the sidewall having the signal information recorded thereon; and detecting the tilt quantity on the basis of the amplitude of the detected signal detected.
In the tilt detection method according to the present invention, the tilt quantity is detected on the basis of the return light from the signal information recording sidewall of the disc-shaped recording medium.
Moreover, a recording medium driving device according to the present invention is adapted for rotationally driving a disc-shaped recording medium having a signal information recording sidewall on which signal information that can be discriminated from recording data is recorded, and recording and/or reproducing digital data to and/or from the disc-shaped recording medium. The device comprises: optical pickup means for casting a laser beam formed by a main beam spot and two sub-beam spots onto the disc-shaped recording medium and receiving a return light reflected and diffracted on the surface of the disc-shaped recording medium; amplitude detection means for detecting the amplitude of a signal based on a return light of two target beam spots, of the main beam spot and two sub-beam spots, from the signal information recording sidewall; and tilt detection means for detecting the tilt quantity on the basis of the amplitude of the signal detected by the amplitude detection means.
In the recording medium driving device according to the present invention, a laser beam formed by a main beam spot and two sub-beam spots is cast onto the disc-shaped recording medium by the optical pickup means, and the tilt quantity is detected by the tilt detection means on the basis of the amplitude of a signal based on a return light of two target beam spots, of the main beam spot and two sub-beam spots, from the signal information recording sidewall.
Furthermore, a tilt detection method according to the present invention comprises the steps of: casting a laser beam formed by a main beam spot and two sub-beam spots onto a disc-shaped recording medium having a signal information recording sidewall on which signal information that can be discriminated from recording data is recorded, and receiving a return light reflected and diffracted on the surface of the disc-shaped recording medium; detecting the amplitude of a signal based on a return light of two target beam spots, of the main beam spot and two sub-beam spots, from the signal information recording sidewall; and detecting the tilt quantity on the basis of the amplitude of the detected signal.
In the tilt detection method according to the present invention, a laser beam formed by a main beam spot and two sub-beam spots is cast onto the disc-shaped recording medium, and the tilt quantity is detected on the basis of the amplitude of a signal based on a return light of two target beam spots, of the main beam spot and two sub-beam spots, from the signal information recording sidewall.